Abdullah bin Abi Musa al-Nasri said that Sayyidah Aishah (may Allah be pleased with her) said to me: "Do not abandon standing in prayer at night, for the Prophet (peace and blessings be upon him) never abandoned it. When he (peace and blessings be upon him) was ill or weak, he would pray sitting."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4722